1. Field of the Invention
This disclosure relates to a transparent see-through display device, and more particularly, to a device capable of displaying images by allowing background radiation and beams incident to the display device to be exclusively or simultaneously transmitted or blocked.
2. Description of the Related Art
Display devices through which various types of information such as images and characters are visually displayed to human beings have come into the highlight as a core sector in information and communication industries.
In the future, it is expected that displays will require not only conventional ultra-thin, high-resolution and light characteristics but also transparent and flexible characteristics. Particularly, when transparent displays are applied to televisions, monitors, vehicular displays, head-up displays (HUDs) and the like, the ripple effect is enormous. Accordingly, attentions have recently been paid to the transparent displays.
Here, the transparent displays may be used for electronic products, transportation, industry, military and the like. Particularly, when the transparent displays are applied to vehicular windshields, information may be visually displayed through the transparent displays, and electronic devices may be applied to any types of glass, thereby improving security systems and the like. Further, dashboards and navigators may be easily built in vehicular windshields, and glass for aquaria or show windows may be used as displays. When the transparent displays are applied to military fields, they may be applied to goggles for military, through which targets and instructions in front of soldiers are displayed, and the like.
However, it is difficult to implement the transparent displays using current display technologies. A liquid crystal display (LCD) is used to display a specific image by changing arrangement of liquid crystal molecules when beams are supplied to the LCD and radiated to the outside of the LCD. The LCD have been sufficiently developed because current manufacturing techniques are stabilized, large-sized displays are implemented, reliability is secured as commercial displays, and the like.
However, it is difficult to implement transparent displays because of main components such as a back light apparatus and a color filter.
Here, the back light apparatus is divided into a direct light type and a light guide type. The direct light type is a type in which a light source is disposed beneath a light emission surface to have an optical distribution of a surface light source. In the direct light type, several light sources are disposed, thereby improving luminance and broadening a light emitting surface as compared with in the light guide type. However, the surface light emitting source is a problem in implementing a transparent display. On the other hand, the light guide type is a type in which a light guide plate is used to guide beams toward a light emission surface, and a light source is disposed at a side of the light guide plate. In the light guide type, optical patterns are formed to allow luminance to be uniformly distributed on the entire light emitting surface. However, when a diffusion sheet is formed on the light guide plite, the optical patterns cause distortion of transmitted beams, and therefore, it is difficult to implement a transparent display. Since the diffusion sheet diffuses beams, transparency of the light guide plate is considerably lowered. Therefore, the diffusion sheet is a primary factor in blocking implementation of a transparent display.
Further, a color filter of the LCD has a transmittance of 25% or less, and its efficiency is low. For this reason, it is difficult to ensure transparency. The color filter is formed using methods including electrodeposition, printing, dyeing (dyeing of photopolymer patterns), pigment dispersion (photolithography using photopolymer in which pigments are dispersed), and the like. However, the electrodeposition has a critical problem in uniformly arranging pixels and manufacturing large-sized substrates due to inequality of the shape around an electrode. The dyeing is hardly used because it is difficult to align liquid crystal cells at precise positions, it is inaccurate to form patterns, and it is unsuitable for the formation of thin films, the improvement of resolution and the formation of large-sized substrates. While the dyeing has characteristics of precision (high resolution) of pattern formation, high light transmittance, high color purity and the like, the dying has problems of low thermal resistance, low light resistance and low chemical resistance, caused by discoloration or evaporation of the color of a pigment. The pigment dispersion is most suitable out of the aforementioned methods because it does not have such problems. Accordingly, the pigment dispersion has recently been frequently used in manufacturing color filters. However, most beams emitted from a back light are absorbed or reflected by a color filter formed using the pigment dispersion. Therefore, the color filter is a main cause of low optical efficiency and an obstacle in implementing transparent displays.